1. Field of the Invention
This invention relates to a fire alarm system in which terminal units, such as fire detectors, are connected to a receiving portion and the terminal units are given unique addresses so that a particular terminal unit having a status change can be detected.
2. Description of the Related Art
A conventional fire alarm system in which terminal units, such as fire detectors, are connected to a receiving portion thereof, and the terminal units are given unique addresses so that a terminal unit having a status change is detected, has been disclosed in Japanese Patent Laid-Open No. 2-201597. Such a system is capable of enabling the receiving portion to quickly detect a terminal unit among the terminal units that has a status change.
The structure of the foregoing system has an arrangement such that the terminal units are divided into a plurality of groups. The timings at which the terminal units respond to the receiving portion are made to be different among the groups of the terminal units. A terminal unit having a status change responds to the receiving portion (system polling) at a response timing for the group to which the terminal unit having the status change belongs. Timings at which terminal units belonging to the group to which the terminal unit that has responded to the receiving portion at the system polling belongs, are made to be different among the terminal units in the group. The terminal unit having the status change responds to the receiving portion at the response timing for the terminal unit (point polling), and the receiving portion collects specific information from the terminal unit that has responded to the receiving portion at the point polling (selecting).
Thus, the operation for obtaining predetermined information is performed for only the terminal unit having the status change. The operation for obtaining the predetermined information is not performed for the terminal units that are free from status changes. Therefore, the status change of a terminal unit can be detected in a shorter time as compared with a structure in which the predetermined information is intended to be sequentially obtained from all terminal units.
The foregoing terminal units which are connected to the receiving portion are fire detectors, smoke blocking and exhausting units and transmitters. If the transmitter is operated, a fire alarm is generated within a predetermined time from the commencement of the operation and a response lamp of the transmitter that has been operated must be turned on. If many terminal units have status changes in a system comprising a multiplicity of terminal units, there is a risk that the fire alarm cannot be generated within the predetermined time.
In a case where 256 terminal units are divided into, for example, four groups, polling is performed for each of the four groups and all four groups have responded to the polling (a status change that does not relate to a fire is included), point polling must be performed for all four groups. If many terminal units in one group have status changes, all the terminal units having the status changes must be subjected to the selecting operation so that the receiving portion collects predetermined information from each of the terminal units.
In the above example, if the operated transmitter belongs to, for example, the fourth group, information collection starts at the terminal unit (the terminal unit having the status change) belonging to the first group and therefore a problem occurs in that a long time is required to collect information from the transmitter after commencement of the information collection from the terminal unit belonging to the first group.
Also the fire detectors, gas detectors and the like that are connected together with the terminal units to be controlled have a similar problem in that a long time is required to collect information from a fire detector or a gas detector having a status change after commencement of the information collection from the terminal unit belonging to the first group and arranged to be linked to a smoke blocking and exhausting unit.
The fire detectors include, in its category, non-accumulative type fire detectors having no accumulating function. The system having the non-accumulative type fire detector has an arrangement such that the fire receiver performs the accumulating operation. That is, the fire receiver checks the level of the fire detector at each predetermined timing after the fire receiver has discriminated that the fire detector had detected a level higher than a fire level, accumulation of the fire detector is completed if the number of times exceeding the predetermined level is larger than a predetermined number of times, and a discrimination is made that a fire has been detected and thus the alarming operation is completed. After the accumulation has been completed, the operation of the fire detector has been determined. Therefore, the receiver does not need to collect information from the fire detector.
It the detected smoke density is lower than a fire level though the operation of the fire detector has been determined, a discrimination is made that the status of the fire detector has been changed. Since the foregoing conventional system has the arrangement such that a response to the fire receiver is made when the status of the fire detector has been changed, a response to the fire receiver is undesirably made even if a state of non-fire phenomenon has been restored. As a result, if the detected smoke density is lower than the fire level, a response to the fire receiver is undesirably repeated. If the detected smoke density is raised higher than the fire level, the fire detector discriminates that the status has been changed and responds to the receiver.
If the detected smoke density is repeatedly raised and lowered in the vicinity of the fire level even after the operation of the fire detector has been determined and the fire receiver has issued an alarm in response to the fire detector, the fire detector frequently responds to the fire receiver. Thus, the number of the responses to the fire receiver becomes too large and therefore the process to be performed by the fire receiver is undesirably delayed.
The accumulative type fire detector has an arrangement such that the fire detector performs the accumulating operation and the operation is determined in response to the fire receiver after the accumulation has been completed. If the detected smoke density is lower than the fire level afterwards, the status is changed and a response to the fire receiver is made. If the detected smoke density is raised afterwards higher than the fire level, the accumulation is again started. After the accumulation has been completed, a response to the fire receiver is made. Therefore, the accumulative type fire detector also experiences the problem of repetition resulting from the rising and lowering of the detected smoke density in the vicinity of the fire level. This repetition undesirably increases the number of response times to the fire receiver and thus the process to be performed by the fire receiver is critically delayed.
The transmitter is the same as the accumulative fire detector from the viewpoint that the operation has been determined when it transmits the response signal to the fire receiver. Therefore, the transmitter has a problem similar to that of the accumulative type fire detector. That is, a discrimination is made that the status of the transmitter is changed if the switch is switched off after the switch has been switched on. Thus, the transmitter responds to the fire receiver and again responds to the fire receiver if the switch is again switched on. As a result, the repetitive switching of the switch of the transmitter undesirably increases the number of response times to the fire receiver and thus a problem arises in that the process to be performed by the fire receiver is delayed.
The fire detectors which are connected to the fire receiver include a multi-signal-type fire detector having at least two fire levels of the following three levels: a fire level 1 (a level in which a fire is discriminated if a smoke density converted into an obscuration ratio is 5%/m), a fire level 2 (a level in which a fire is discriminated if a smoke density is 10%/m) and a fire level 3 (level in which a fire is discriminated if a smoke density is 15%/m). In the case in which the fire detector transmits a signal corresponding to the fire levels 2 and 3 and as well as in a case where the fire receiver is arranged to discriminate a fire when, for example, the fire level 2 is realized, the fire detector transmits a signal denoting the fire level 2 and the operation is discriminated with the fire level 2 after the smoke density has been raised gradually. If the smoke density is later raised to reach the fire level 3, the fire detector again responds to the fire receiver. Also in this case, the number of responses to the fire receiver is increased undesirably and a problem arises in that the process to be performed by the fire receiver is critically delayed. A similar problem arises in the case where a phenomenon, such as heat, light, gas or smell is detected.
Since the conventional system issues a fire alarm only when the fire level transmitted from the fire detector ha s been raised to the level set in the fire detector, a desire to detect a fire prior to the foregoing moment cannot be satisfied.
The value of the smoke density to be detected by the multi-signal-type fire detector is not monotone-increased even in an increase tendency and usually repeats increases and decreases in the form of waves. The detected smoke density is sometimes raised and lowered in the vicinity of the fire level. In the foregoing case, if the detected smoke density exceeds the fire level, the fire detector experiences a status change and responds to the fire receiver. If the detected smoke density is lower than the fire level, the fire detector will have a status change and will respond to the fire receiver. The foregoing operations are repeated. Therefore, the repetitive rising and lowering of the detected smoke density in the vicinity of the fire level excessively increases the number of responses made to the fire receiver.
If a desired fire level for the multi-signal-type fire detector is the fire level 2, a response to the fire receiver is made when the fire level 1 has been realized in a case where the smoke density is raised gradually. If the detected smoke density repeatedly rises and lowers in the vicinity of the fire level 1 (the multi-signal-type fire detector is repeatedly turned on/off at the fire level 1), the number of responses to the fire receiver is increased excessively and a problem arises in that the process to be performed by the fire receiver is delayed. A similar problem arises in the case where heat, light, gas or smell is detected to discriminate a fire phenomenon.
In a case where the accumulating function is exhibited at the detection of a fire by causing the fire detector to have the accumulating function, a problem arises in that the number of parts of the fire detector increases excessively because the parts for the accumulating function must be provided. In addition, a memory capacity required to perform the accumulating operation must be provided for the fire detector. That is, a problem arises in that the fire detector must have a large memory capacity.
In a case in which the conventional system has the arrangement such that the address to be given to the terminal units is composed of, for example, 8 bits, 256 addresses can be created. Thus, a maximum of 256 terminal units each having an inspection function can be used.
If a fire alarm system having greater than 256 terminal units is desired, the 8-bit address will be insufficient to constitute the system. Thus, 9 bits or more must be provided for forming the addresses and a longer time would be required to call each address. Since a microprocessor is usually operated in units of 8 bits, use of incomplete bits, such as 9 bits or 10 bits, poses a problem in that a uniform process cannot easily be performed.
As described above, the conventional fire alarm systems experience the foregoing problems.